Growing plants need nitrogen. Plants such as maize (Indian corn) require a substantial quantity of nitrogen. The soil corn plants grow in obtain nitrogen from legumes such as soybeans, from snow and from other sources. Excess nitrogen will reduce yield of crops such as corn. Insufficient nitrogen will also reduce crop yield. Water used to irrigate plants generally contains minimal nitrogen.
Anhydrous ammonia has been used for many years to provide nitrogen. The anhydrous ammonia is injected into the ground as a liquid or vapor. Injection of anhydrous ammonia into soil is subject to a number of problems. Determining the quantity of nitrogen to be added is complicated by the fact that a substantial quantity of nitrogen may be stored in the soil. Soil samples are required to determine the status of stored nitrogen that is available. The soil samples often indicate that the distribution of stored nitrogen varies from one location to another in each farm field.
The cost of anhydrous ammonia has increased overtime due in part to the increased use by farmers around the planet. Farmers have in the past applied anhydrous ammonia and other fertilizers to maximize crop yield. Farmers are forced today to consider the costs and reduce the use of anhydrous ammonia and other fertilizers, when the cost of additional fertilizers exceeds the value of a minimal increase in crop production.
The loss of anhydrous ammonia needs to be limited to the extent possible. The over application in some areas of each field also needs to be limited or even eliminated.
The change in some anhydrous ammonia from a liquid to a vapor makes accurate control of the application rate difficult. Vapor separated from the liquid results in the over application rate in some areas. The separation of vapor may also result in the loss of some anhydrous ammonia.
Increased pressure in an anhydrous ammonia application system can keep the pressure of the liquid above the vapor pressure of the liquid at ambient temperature. However, a pump in the supply system between a nurse tank and liquid discharge nozzle will create a pressure drop on the pump inlet side. This pressure drop will at times produce vapor. The anhydrous ammonia vapor will prevent accurate metering of a liquid and vapor mixture. Separation of the vapor generally results in a loss of some anhydrous ammonia.
Reducing the temperature in an anhydrous ammonia application system can keep the temperature of the liquid below the temperature at which vapor could be formed. Temperature lowering is obtained by bleeding off some liquid, expanding the liquid into a cold vapor and passing the cold vapor through a heat exchanger. Anhydrous ammonia liquid passing through the heat exchanger is cooled. The vapor discharged from the heat exchanger is then injected into the ground. The vapor is not completely lost. However, some anhydrous ammonia vapor is added to one of several plant rows that also has a metered quantity of liquid anhydrous ammonia. The additional anhydrous ammonia from vapor may provide excess nitrogen to one crop row and may reduce crop yield in that crop row.
Anhydrous ammonia application systems with or without pumps as well as systems with or without cooling systems often include a flow sensor that measures the total flow rate. These systems include a servo valve that controls the total flow rate. A manifold divides the flow of anhydrous ammonia to soil cutting knives. The servo valve reduces the pressure of discharged anhydrous ammonia and may create some vapor. Vapor mixed with liquid anhydrous ammonia will result in an unequal flow from a manifold down stream from a servo valve or other flow control device.